How to use c++ thingie called “Span”

Question

How to use c++ thingie called “Span”

Bryan Kelly 486

Windows 11, Visual Studio 2019, C++, Base58 encoder
I am trying to incorporate functions to do Base58 encoding and decoding. They are widely used by Bitcoin.
The code I am trying is here: https://github.com/bitcoin/bitcoin/blob/master/src/base58.cpp
I have added several includes and down to one error in three places. Example:

std::string EncodeBase58(Span<const unsigned char> input)

I have gone through several variations to include std::span and gsl::span and none are accepted. I “think” I can remove it by replacing the argument with the specified array plus a size_t argument for the size. But, I would like to keep it as is.
What is the right configuration for VS 2019 C++?

PS: The tool to add a hyperlink uses http:// Maybe update it to https://

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Answer 1

RLWA32 49,551

Did you remember to set /std:c++20 for all platform/configuration conbinations? If you did not it's possible that what you see for your project is because the platform/configuration that you're looking at doesn't have the proper setting.

Answer 2

RLWA32 49,551

C++ is case sensitive. Use span, not Span.

Answer 3

Marius H 1

They use their own implementation located at bitcoin/blob/master/src/span.h.

Answer 4

Bryan Kelly 486

Well now.
I read that using span reduces argument from something like:

function( &array, size )
to
function( span<type> input );

But after seeing all that code, I wonder if it is really worth that much effort.
Some advantages are described in some web pages, but I lack the experience to understand the significant improvement.

Thank you for the info.

Answer 5

I am running VS 2019 version 16.11.20.
from this page: msvcs-stl-completes-stdc20

and this quote:

We previously announced that MSVC had completed all features in C++20 for Visual Studio version 16.11.0, and that we had added the /std:c++20 option to indicate that most C++20 features were stabilized and considered production-ready.

And from a few searches it seems that the "span" feature is part of C++20. But my VS is not recognizing the key word span. Below are a few lines from a dot h file.

What steps are needed to recognize this feature?

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How to use c++ thingie called “Span”

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